list builtins done

I think the DTB section on RIF lists [1] is now ready for review for
Last Call.  A few notes and questions:

   * I removed the func:delete function, because 
          (a) it's not in xpath,
          (b) it's confusingly similar to func:remove, and
          (c) it's trivial emulated:  
                func:delete(L, I) = func:except(L, func:make-list(I))

     Some other functions are trivial emulated, but they're in xpath.  I
     think the bar is higher for us adding functions.  This way, the
     only ones we're adding are is-list, list-contains, make-list, and
     get.  list-contains is that only the can be emulated:
             list-contains(L, I) iff count(index-of(L, I)) > 0 
     but I think we specifically discussed that and agreed it was
     worthwhile to have list-contains.

     Obviously, if someone actually wants it, I'm okay with putting
     func:delete back in.

   * This section has examples.  I could trivially suppress them for now
     (this wiki-text is generated by a program [2]), if they bother
     people.  I like them.  They have all been checked by my demo code
     [3].  I'm willing to make similar examples for the rest of DTB for
     a later edition.

   * I don't know the right binding pattern for list-contains.  Above, I
     was assuming it was (b,b), but I can imagine some utility to all
     binding patterns, and at least (b,u) seems pretty reasonable.  It's
     not clear to me whether PR systems would do what I'm imagining with
     that, but it'd be nice to write rules like:

         forall M (        
           if   list-contains(eg:list_of_friends, M)
           then eg:is_friend(M)

     Without it, I guess you'd need some much more cumbersome
     tail-recursive rules like this:

         forall L M (
           if   friend_list(L) and
                get(L, 0) = M
           then eg:is_friend(M)
         forall L  (
           if   friend_list(L) and
                count(L) > 0
           then friend_list(sublist(L, 1))

     PR folks, what do you want, there?

I think that it.  This complete ACTION-760.
     -- Sandro


Received on Tuesday, 5 May 2009 20:42:04 UTC